<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>css3圆角</title>
	<style type="text/css">
		.box{
			width: 200px;
			height: 200px;
			border:2px solid #000;
			background-color: gold;
			margin: 50px auto 0;
			/*border-top-left-radius: 100px 50px;*/  /*也就是上面100px，左边50px，就会变成一个弧*/ 

			/*border-top-left-radius: 100px;*/ /*相等时就成了一个正圆*/
			/*border-top-right-radius: 100px;*/

			/*border-radius: 40px;*/

			border-radius: 50%;
		}
	</style>
</head>
<body>
	<div class="box">
		
	</div>
</body>
</html>